It has long been known that internal combustion gasoline or diesel engines must be protected from impurities in air inducted into the engine for combustion. Filters have been developed and are quite efficient for removal of solid particles. Liquid impurities, however, are much more difficult to remove.
In a typical system, a snorkel pipe extending vertically behind the truck cab is open to receive air at the top of the cab and direct it downwardly through the pipe and beneath the cab along a torturous path to the engine filter. The elimination of moisture from such systems has often been provided by a hood or cap at the top of the snorkel pipe, or by filters or restrictions in the snorkel pipe itself. The restrictions are frequently in the form of cross sectional narrowings, configuration changes or tangentially directed veins which cooperate to create a centrifical separation of moisture from air. U.S. Pat. No. 4,366,878 is exemplary of this type of system. Air is received above the cab at a cap opening forwardly. A long snorkel pipe extends from the upper cap downwardly to a foot pipe generally beneath the cab. An additional conduit directs air from the foot pipe to the air cleaner. The foot pipe provides a change of direction from the vertical to the horizontal, as well as a change of configuration from rectangular to cylindrical. The foot pipe includes a low portion with drain means for collecting and draining water. The general idea is that the long free fall in the vertical pipe aided by the change of direction at the bottom of the vertical pipe causes moisture to be directed to the low portion and eliminated at the drain means.
A system intended to eliminate moisture at the air entry cap is exemplified in U.S. Pat. No. 4,212,659. Air enters the cap above a cab before being directed down a vertical pipe behind the cab and then forwardly under the cab to the air cleaner and engine. Air enters a downwardly directed opening and passes through a plurality of parallel vanes having a change of direction in them. Air is directed through the vanes and upwardly against the top of the cap and then is eventually forced downwardly into the vertical pipe. The torturous path causes moisture to gather on the top of the cap and flow down the sides or fall by gravity into annular water traps having discharge openings.
As recognized in the first of the above discussed patents, attempts to eliminate moisture at or near the air cleaner have been unsatisfactory and, therefore, it has been preferred to remove water well upstream from the air cleaner. The present invention, however, is directed to a duct configuration which achieves water elimination near the air cleaner.